1. Field of the Invention
The present invention generally relates to circuits for connecting communication lines with a terminal, and particularly relates to a circuit which connects communication lines with a terminal when a point-to-multipoint connection is established in a communication system such as a SDH-ring system.
2. Description of the Related Art
FIG. 1 is an illustrative drawing showing an example of an SDH-ring system. The SDH-ring system of FIG. 1 includes communication lines (SDH ring) 500, a plurality of LSIs 501, and a plurality of terminals 502 connected to the communication lines 500 via a corresponding one of the LSIs 501. The LSIs 501 receives data transmitted via the communication lines 500, and outputs the data to the terminals 502. The terminals 502 are devices such as a PBX, an ISDN-TD, or the like, to which a telephone, a TV set, etc., can be connected.
The simplest configuration to achieve a point-to-multipoint connection is to use a fixed communication baud rate in each of the terminals 502. In order to have simultaneous communication with as many terminals 502 as possible, the communication lines 500 must be provided with channels in the same number as the number of terminal channels defined by a terminal format.
In detail, a frame pulse XHF0/1 is used for indicating a start timing of each frame of communication data, and a HW (highway:communication line) clock HWC0/1 is used for establishing synchronization with a plurality of time slots contained in each frame. Each time slot is comprised of 8-bit data, and 32 time slots, for example, together make up one frame. In one frame, one or more time slots are put together to form a channel. When a communication baud rate is fixed and 8 channels are present, for example, each channel is comprised of 4 time slots. Each channel is called a path, and each path is used for communicating with a corresponding one of the terminals. Within one frame, an order of the path is not restricted but free to be set, and the order can be path 1, path 7, path 3, path 5, . . . , and so on, for example.
The start timing of each path on the side of the communication lines 500 is indicated by an offset number which is obtained by counting the number of pulses of HW clock HWC0/1 from the timing of the frame pulse XHF0/1. This offset number is stored in a register inside each LSI 501. In the case of a fixed communication baud rate, therefore, a fixed number of time slots starting from a timing indicated by the offset number are read from the communication lines 500, and are output to the terminal. Namely, when the communication baud rate is fixed to four time slots, for example, arrival of the path 1 results in writing data in addresses 0 through 3 of the output to the terminal, and the arrival of the path 3 leads to writing data in addresses 8 through 11. Such processing is conducted with regard to each path so as to output each path in a predetermined order to the terminal 502. In this case, the LSI 501 can be implemented by using a simple configuration.
When a communication baud rate is different for each path, however, the number of time slots varies for different paths. In this case, a simple process as described above is not applicable when paths arranged in an order of free choice on the side of the communication lines 500 need to be output to the terminal 502 in the order of path numbers. The communication baud rate (the number of time slots) of each path is stored in the register inside the LSI 501, as described above. The communication baud rate thus may be decoded with respect to each path so as to control a position of data writing, so that data of each path is written at an appropriate address position in the output to the terminal. Such a process, however, requires a complex and large circuit structure, resulting in an undesirable enlargement of a circuit size of the LSI 501.
Accordingly, there is a need for a small-scale circuit which can output data of paths to the terminal by using a simple process when the paths are provided in an order of free choice on the side of the communication lines in a system employing a point-to-multipoint connection and an adjustable communication baud rate.
Accordingly, it is a general object of the present invention to provide a small-scale circuit which can satisfy the need described above.
It is another and more specific object of the present invention to provide a small-scale circuit which can output data of paths to the terminal by using a simple process when the paths are provided in an order of free choice on the side of the communication lines in a system employing a point-to-multipoint connection and an adjustable communication baud rate.
In order to achieve the above objects according to the present invention, a device for outputting paths to a terminal after rearranging the paths when the paths are arranged in an order of free choice on a side of communication line includes a counter which receives a path number of a path in response to first data of the path, and counts up a count starting from the path number in response to second and following data of the path. The device further includes a storage unit which stores real data of the path at positions indicated by the count, wherein the real data stored in the storage unit is output to the terminal.
In the device described above, the real data of the path is written at positions controlled by the counter, so that terminal-side output is obtained such that the real data of path n holds an output position thereof in the n-th and following time slots. In this manner, a simple process and a simple circuit based on path numbers can rearrange communication-line data into terminal-side data.
According to one aspect of the present invention, the device further includes a data-enable circuit which holds 1 at positions therein indicated by the count when the real data is written at the positions indicated by the count in the storage unit, wherein the data-enable circuit holds zero at all positions therein at an initial state with respect to each frame.
In the device described above, the data xe2x80x9c1xe2x80x9d is set in the data-enable circuit so as to correspond, in terms of positions thereof, to the read data output to the terminal. In this manner, data for indicating a valid/invalid status of each time slot can be readily obtained with regard to the real data output to the terminal.
According to another aspect of the present invention, the device further includes a circuit which masks the real data output to the terminal by using data held in the data-enable circuit.
In the device described above, a valid/invalid status of each time slot can be found by using the data-enable circuit, so that invalid data can be masked so as not to be output.
According to another aspect of the present invention, the device further includes control-information-allocation circuit which receives control information allocated to the paths, and outputs the control information to the terminal in synchronism with the real data output to the terminal.
In the device described above, control information such as error information contained in paths can be output to the terminal in synchronism with the real data.
According to another aspect of the present invention, the control-information-allocation circuit includes a plurality of selectors which are connected in series such that one of the selectors receives as one of inputs thereof an output from a preceding one of the selectors.
In the device described above, the circuit comprised of the plurality of selectors can allocate the control information.
According to another aspect of the present invention, each of the plurality of selectors selects either the output from the preceding one of the selectors or the control information on a corresponding path, depending on whether a communication-data rate of the corresponding path is zero.
In the device described above, the circuit comprised of the plurality of selectors can allocate the control information by using the communication-data rate.
According to another aspect of the present invention, the device further includes a data-enable circuit which holds 1 at positions therein indicated by the count when the real data is written at the positions indicated by the count in the storage unit, wherein the data-enable circuit holds zero at all positions therein at an initial state with respect to each frame.
In the device described above, the data xe2x80x9c1xe2x80x9d is set in the data-enable circuit so as to correspond, in terms of positions thereof, to the read data output to the terminal. In this manner, data for indicating a valid/invalid status of each time slot can be readily obtained with regard to the real data output to the terminal.
According to another aspect of the present invention, the device further includes a circuit which masks the control information output to the terminal by using data held in the data-enable circuit.
In the device described above, a valid/invalid status of each time slot can be found by using the data-enable circuit, so that invalid data can be masked so as not to be output.
According to another aspect of the present invention, the device further includes a frame buffer which holds the real data for at least one frame period.
In the device described above, the frame buffer can hold an amount of the real data commensurate with one frame.
According to another aspect of the present invention, the device further includes a converting circuit which converts an output of the frame buffer from parallel data to serial data, the serial data being output to the terminal.
In the device described above, the parallel output from the frame buffer can be converted into the serial data before being output to the terminal.
According to another aspect of the present invention, a device is presented for outputting real data of paths to a terminal at terminal-output data positions corresponding to path numbers of the paths when receiving the paths arranged in an order of free choice on a side of communication line, and for outputting multiplexed signaling information contained in the paths in a form of multi-frames to the terminal. The device includes a write-signal-generation circuit which generates write signals with respect to each path by detecting synchronization of the multi-frames, a rotation shifter which performs a rotation shift of a predetermined number of signaling signals contained in each frame of the multi-frames in accordance with the path numbers, a write-signal-control circuit which selects at least one of the write signals in accordance with the path numbers, and a storage unit which stores outputs from the rotation shifter at positions indicated by the write signals selected by the write-signal-control circuit.
In the device described above, when the signaling signals are supplied in the form of multi-frames during the multiplexed signaling mode, the signaling signals can be output to the terminal so as to have positions thereof corresponding to those of the real data of each path which is also output to the terminal.
According to another aspect of the present invention, the rotation shifter performs a rotation shift of the predetermined number of signaling signals by {(a path numberxe2x88x921)%(the predetermined number)} bits.
In the device described above, the signaling signals can be allocated at appropriate positions in the storage unit.
According to another aspect of the present invention, the write-signal-control circuit comprises a plurality of selectors connected in series such that one of the selectors receives as one of inputs thereof an output from a preceding one of the selectors, each of the selectors having {(a corresponding path numberxe2x88x921)/(the predetermined number)+2} inputs.
In the device described above, the plurality of selectors connected in series such that one of the selectors receives as one of inputs thereof an output from a preceding one of the selectors is used for selecting the write signals, thereby allocating the signaling signals at appropriate positions in the storage unit.
According to another aspect of the present invention, each of the selectors comprises a 2-input selector and 3-input selectors provided in a total number of {(the corresponding path numberxe2x88x921)/(the predetermined number)+1}.
In the device describe above, the write-signal-control circuit can be implemented by using a 2-input selector and a plurality of 3-input selectors.
According to another aspect of the present invention, each of the selectors comprises 2-input selectors provided in a total number of {(the corresponding path numberxe2x88x921)/(the predetermined number)+1}.
In the device describe above, the write-signal-control circuit can be implemented by using a plurality of 2-input selectors.
According to another aspect of the present invention, the device further includes a register which sets mode information with respect to each path, the mode information indicating one of a normal signaling mode and a multiplexed signaling mode, and a selector which receiving the signaling signals corresponding to the multiplexed signaling mode as first inputs and the signaling signals contained in attached information of the paths corresponding to the normal signaling mode as second inputs, and selects one of the first inputs and the second inputs based on the mode information set in the register.
In the device described above, one of the multiplexed signaling mode and the normal signaling mode can be indicated with respect to each different path, so that the multiplexed signaling mode and the normal signaling mode are allowed to coexist.
According to another aspect of the present invention, the device further includes signal-allocation circuit which receives the signaling signals contained in the attached information, and outputs the signaling signals contained in the attached information to the terminal in synchronism with the real data output to the terminal.
In the device described above, the signaling signals contained in the attached information of the paths can be output to the terminal in synchronism with the real data.
According to another aspect of the present invention, the signal-allocation circuit comprises a plurality of selectors which are connected in series such that one of the selectors receives as one of inputs thereof an output from a preceding one of the selectors.
In the device described above, the circuit comprised of the plurality of selectors can allocate the signaling signals contained in the attached information.
According to another aspect of the present invention, each of the plurality of selectors selects either the output from the preceding one of the selectors or a signaling signal contained in the attached information of a corresponding path, depending on whether a communication-data rate of the corresponding path is zero.
In the device described above, the circuit comprised of the plurality of selectors can allocate the signaling signal(s) by using the communication-data rate.
According to another aspect of the present invention, the device further includes mode-information-allocation circuit which receives the mode information from the register, and outputs the mode information to the terminal in synchronism with the real data output to the terminal.
In the device described above, the mode information stored in the register with respect to each path can be output to the terminal in synchronism with the real data.
According to another aspect of the present invention, the mode-information-allocation circuit comprises a plurality of selectors which are connected in series such that one of the selectors receives as one of inputs thereof an output from a preceding one of the selectors.
In the device described above, the circuit comprised of the plurality of selectors can allocate the mode information.
According to another aspect of the present invention, each of the plurality of selectors selects either the output from the preceding one of the selectors or the mode information of a corresponding path, depending on whether a communication-data rate of the corresponding path is zero.
In the device described above, the circuit comprised of the plurality of selectors can allocate the mode information by using the communication-data rate.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.